1) Field of the Invention
The present invention relates generally to an improved system for hydraulic control of a towed implement utilizing the tractor hitch control.
2) Related Art
Numerous systems have been proposed for utilizing the tractor hitch control for controlling a towed implement. For example, U.S. Pat. No. 3,627,053 shows a system wherein the hitch control valve and a selector valve control a remote cylinder of a towed implement. A system for automatically raising the tractor hitch to a non-interfering position and controlling a trailing implement cylinder when SCV control is shifted from the rockshaft cylinder to the trailing implement is shown in U.S. Pat. No. 5,152,347 of common ownership with the present invention. An electronic control unit (ECU) such as shown and described in U.S. Pat. No. 4,979,092 is utilized to control the trailing implement in response to input signals including a lever control signal, a position sensor signal and a draft force sensor signal. When the control input from the implement is plugged into the ECU, control is shut off to the 3-point hitch and automatically transferred to the trailing implement. Both a manually operated selector valve and at least one tractor selective control valve (SCV) are required in the system shown in U.S. Pat. No. 5,152,347.
When the ECU system is utilized with a typical lift and depth control arrangement such as for a disk harrow, the hydraulic cylinder on the implement operates as a one-way single acting cylinder with the hitch control valve functioning as a three-way valve wherein implement weight causes the cylinder to retract so the frame moves downwardly to the field-operating position. One problem with one-way operation is that the operator is unable to raise the wheels from ground contact when it is desirable to do so, for example, when the additional weight of the wheels could be used to assist tool penetration in certain ground conditions.